Thursday, May 27, 2010

Thermosyphon systems use the lower density of the water heated by the collector to drive water circulation around the collector and tank circuit. The systems are simpler than most solar water heating systems in that the need for both a circulation pump and a controller are replaced by the thermosyphon natural circulation.

As the schematic above shows, the only conponents of the system are the collector, the storage tank, and the connecting plumbing -- sun and gravity takes care of the rest. The system is simpler, less costly, and lower maintenance than most solar water heating systems.

Lonnie did a very nice job on this system, and provides full construction detail. While the collector construction follows the general design of the $1K collectors, Lonnie includes some new wrinkles in the collector that should improve performance.

While thermosyphon systems are very straight forward and simple, there are some things that must be kept in mind:

The tank must be above the top of the collector. This allows the hotter water in the collector to rise upward into the tank. It also automatically shuts off the circulation when the water in the collector cools below the tank temperature.

The plumbing between the collector and tank must slope upward toward the tank. And, since the thermosyphon forces driving the flow are relatively weak, the collector and connecting plumbing should have low flow resistance.

This thermosyphon design does not include freeze protection, so is only for situations in which no freezing weather occurs, or the collector can be drained for the winter. There are thermosyphon designs that circulate antifreeze through the collector and use a heat exchanger to transfer the collector heat to the storage tank.

If you can meet the above criteria, the thermosyphon systems are a good choice for simple, cost effective, and maintenance free solar water heating.

Tuesday, May 25, 2010

We purchased a new TV a few weeks ago, and I thought I would pass on some of what we learned along the route to trying to find an energy efficient TV that was also a step up in picture size and quality. The TV we replaced is a 10 year old Toshiba 34 inch CRT style TV. While the TV was showing some signs of age, it was still serviceable, and we did find a good home for it over the FreeCycle Program. After quite a bit of thought and looking, we replaced it with a 46 inch Sharp LC-46LE700UN. The material below says how we got there and gives some (hopefully) helpful resources if you are searching for a new TV.

Bottom Line messages from this quest for an efficient new TV:

TV's vary a lot in power use, and most people watch them enough that they are a major user of power in the home, so shopping for a low energy use TV can save a lot of energy and carbon over the life of the TV.

Its not that easy to get actual power use numbers for TV's, but if you use some of the resources listed below, you can easily find a TV that uses (roughly) half as much power as its next door neighbor on the store shelf, and has just as good (or better) a picture. You will likely have to pay a bit more for it, but the energy savings over the life of the TV will pay you back, and you can save a lot of carbon emissions.

Energy Star labels are not very helpful in their current form.

Features

We decided that the new TV for us should be:

Energy efficient

Have a screen size around 45 inches for our room size and viewing distance.

Support HD TV.

Have high picture quality in a bright room

Energy Use

One objective we have is that any new item that comes into the house has to use less power than the item it replaced -- preferably a lot less. We also try hard to get close to the lowest power use designs available without spending the price through the roof. This is part of our long range plan to get down to zero net electricity with the modest size PV array that we have. Basically, our use was about 1000 KWH a month a couple years ago and we cut this down to 500 KWH a month via conservation and efficiency measures that are part of our Half Program. We then added a 2150 watt PV array that we expect to cut our net usage by about 250 KWH a month. So, to eventually get down to net zero electricity use, we have to cut our monthly consumption by another 250 KWH through further conservation and efficiency improvements.

Our old set used 148 watts in steady use as measured by a KillAWatt meter. So, the objective was to get a somewhat larger screen set that did HD and used substantially less power. This seems like a fairly tall order in that larger screen sets generally use more power and we wanted to increase screen size, but it turns out to be very doable due to improvements in TV energy efficiency and to recent developments in LCD backlighting.

Resources For TV Selection

It is not that easy to find good energy use data for TV's. Even the models that are efficient tend to be rather vague about how much less power they use. Statements like "uses 30% less power" are tacked on some models, but 30% less than what?

These are some resources we found to be helpful (if you know of others, please let me know):

Energy Star Labels
Energy Star provides labels on some sets that meet their current criteria for low power consumption -- generally the label means that the set might use at least 20% or 30% less than an average model in its size class (or something like that -- varies with the appliance and time).

We found the Energy Star labels to be more or less useless because:
1) they are awarded by screen size class, so a large screen set with an Energy Star label uses a lot more power than a smaller screen set with the label. I really want to know how much power a set actually uses, not that it uses somewhat less power than the other energy hogs in its size class.
To me this use of screen size classes is a flawed idea -- It would be kind of like giving a Hummer an Energy Star label because it has the best fuel economy of the Ultra Pig class. It hides the basic truth that larger screen TV's use more power.
2) the Energy Star label requirements can be very flaky. Up until recently TV sets were only rated on how much power they used when they were turned off!
3) I guess the Energy Star folks think we are too dumb to know what a watt is, and are trying to get to something that is easier to understand, but to me the label just hides important information.
Oddly, the Energy Star yellow labels that are required for all clothes washers and refrigerators provide all the information you need on a simple and easy to use label -- no idea why we can't get this on TV's, which can actually use more power than a fridge.

Consumer Reports
Consumer Reports magazine (or the website) gives some useful info on TVs.
Unfortunately they just give you a poor -> good rating scale on energy use without giving specific numbers. And, they don't provide any information on how they go about determining the energy use rating.

CNET Reviews
I found the CNET reviews the be the most helpful resource for information on how the sets perform visually, and on their energy use.
They have a good review process that includes energy use numbers for various viewing modes.

KillAWatt
At one point when we were getting a bit frustrated with trying to find actual power use numbers for some sets we were interesting in, we actually brought along a KillAWatt to the store to measure power use. The store people were very cooperative in this -- no push-back at all.
The down side of doing it this way is that many sets have a "store mode" that that the set can be put on that is intended to provide a very bright picture for in store comparisons of picture quality. This "store mode" uses more power, and can be a bit misleading.

What We Picked

As it turned out, for LCD sets the big recent development that does make a significant difference in power consumption is the LED backlight. The sets with LED backlights use substantially less power than sets with the still more common fluorescent backlights.

At this time, you do pay a cost premium for the LED backlighting. In our case, the LED backlit models were about $200 more than similar performance models with fluorescent backlights. But, we believe (based on actual power measurements) that over the life of the set and with our viewing habits, the power saving at current utility rates would pay back the extra with a bit of interest, and the carbon emissions saving over the life of the set is significant.

LED backlit sets also have a much longer life -- long enough so that its unlikely you will ever have to replace a backlight.

While LED backlit sets as a class have lower power consumption, there is still a significant difference in power use between the various LED backlit models. So, it still pays to look into actual power use of the sets you are considering even if they are all LED backlit.

The set we got has a feature that adjusts the backlight intensity to the room light level. That is, it turns the backlight down when room lighting is lower. I have found that this saves a significant amount of energy -- so, its probably worth looking for these kinds of features.

Power Use

I figure our TV is on around 8 hours a day -- this seems like a lot, but I think its pretty close -- we each tend to want to watch different things and we have digital recorder -- both of these extend the time on.

New Set:

Power use per year = (8 hours/day)(360 day/yr)(68 watts) = 196 KWH per year

Cost of electricity at 11 cents/KWH = $21 per year

CO2 emissions at 1.5 lbs/KWH = 294 lbs of CO2 per year

Compared to the old set, this is a saving of 230 KWH a year, $26 per year, and 350 lbs of CO2 a year.

Its a bit hard to compare the savings for this TV to other new ones out there. But, its certainly safe to say that if you don't consider power usage when you do the selection you could easily end up with power consumption that is more than twice the numbers above -- its important to do your homework.

Findings To Date

We are very very pleased with the new TV.

The picture is just outstanding -- my untrained eye just cannot find any flaws.
My feeling is that some of the places that do TV reviews (including my favorite CNET) obsess over tiny picture quality details that most people will never notice. I think that they don't feel they are earning their paycheck as reviewers if they can't find some flaws in the picture to comment on.

The power consumption is actually lower than anticipated.
The set has this very neat feature that you can enable that adjusts the back light level depending on room light. So, in a bright room with sun streaming in the windows, the power consumption is 83 watts, but as the room gets dimmer because you lower some shades or at night, the power consumption drops all the way down to 51 watts! So, under night viewing conditions, the new 46 inch set uses only about 1/3rd the power that our old 34 inch set used -- nice.

The power use when the set is off is lower than my KillAWatt goes. The CNET labs report says 0.07 watt in standby/sleep mode -- also nice.

The only negative in the whole picture is the amount of work we had to put into finding a set that had very low power consumption and good performance -- its just seems like this should be easier. In particular, it seems like the Energy Star program could be a lot more helpful than it is now. Why can't we have the same kind of label that clothes washing machines and refrigerators have on all devices that use a significant amount of electricity (or any kind of energy)?

Thursday, May 13, 2010

While the system is modeled after our $1K system, Neil has included a number of unique features including a fiberglass tank liner, a very nice large copper coil heat exchanger, integration with a combi boiler system, and a unique design for the collector absorber plate.

Some of the highlights

Tank

The tank is tall with a small footprint in order to take up less floor space.

Instead of using an EPDM membrane for the waterproof liner, Neil used several layers of fiberglass to provide the waterproof lining.

Collector

The collector absorber plate is a unique design that uses a single sheet of aluminum that all of the riser tubes are thermally bonded to.

The thermal bonding is provided by a narrow, grooved strips of aluminum that snap over each riser tube and then riveted to the

full width aluminum sheet.

Heat Exchanger

Neil made a very compact and efficient single pass heat exchanger from copper tubing as shown in this picture.

Monday, May 10, 2010

All Season Solar Cooker
This is a new design for a solar cooker from Jim La Joie. The unique feature of the cooker is that the cooking vessels is always positioned on the flat bottom of the cooker, and the reflective panels are easily repositioned with one motion to focus the sun on the cooking vessel.

This is a bit off topic, but I've been trying to keep track of the spill, and to learn more about offshore drilling/production in more depth than the CNN style reports.
The best place I've found is: www.TheOildDrum.comThe long post by Shelburn is very interesting.

It was a bit of a shock to me to see how much day in and day out risk is inherent in this method of extracting oil.

If you know of other good sources of in-depth information in this area, please leave a comment.

Monday, May 3, 2010

While tracking solar electric (PV) collectors are common, there are not many tracking solar water heating collectors. Here is a nice, simple, inexpensive way to do a tracking water heating collector and gain about 30% on energy collected over a sunny day.

This is a nice job on a heat exchanger made from a large coil of PEX pipe. This heat exchanger sits in the solar heat storage tank. Potable water flows through the PEX coil before going to the water heater and is pre-heated by the solar heated water. All the construction details on this heat exchanger...